That's because, with cab drivers on strike, Uber is stepping in to fill the void. In the United Kingdom, Uber saw an 850 percent signup increase since last Wednesday, the Washington Post reports.

Forbes called it the "Streisand effect," when an attempt to get rid of something has the opposite effect and causes it to get more publicity. In Europe, Uber is not as well known as it is in the United States (where Uber started). But now with taxi companies complaining about it, it gives Uber more publicity in Europe. And that's not a good thing for cab companies if Europeans like the Uber alternative to traditional taxi hailing while trying out the app during the taxi strikes.

Uber is being proactive with taxis on strike by offering discounts in some European cities, Reuters reports.

The [Licensed Taxi Drivers Association] argues that Uber operates in a "grey area" and circumvents current legislation that governs private-hire taxis. Steve McNamara, the LTDA's general secretary, argues that Uber's drivers use a "specific device that's programmed to be a meter" which is therefore illegal under the Private Hire Vehicle Act.

Uber disagrees that the app acts as a meter and points to high consumer demand for the app. As Jo Bertram, the Uber's UK and Ireland general manager told the Telegraph: "The results are clear: London wants Uber in a big way."